Felt Recoil

[errante]

My question is about felt recoil. Is energy (foot pounds) the best indicator of how much recoil the shooter will feel? My Kahr P45 (empty weight with mag 20.5 oz), has a much greater recoil with a 200 grain +P compared to the 230 gr practice load. Here is the data from the manufacturers:
Velocity Energy (foot pounds) Weight
+P 1080 FPS 518 200 grains
810 FPS 335 230 grains

The +P with a lighter bullet has a much higher felt recoil than the 230 gr. So much so, that I would only use that ammo if it was needed. I practice with the non +P 230 grain.

Where I am going with this, if I look at a certain caliber and the energy is higher, would I always expect higher recoil based on energy alone? (Of course using the exact same pistol or revolver). Is there any other factors from a purely ballistic comparison that would affect recoil?

Here is an example of S&W 500 Ammo
Velocity Energy (foot pounds) Weight
1608 2297 400 grains
1667 1696 275 grains

Would the 400 grain bullet have a much higher recoil than the 275 grain bullet? Would that be indicated by the difference in energy? Or only because of the lighter bullet? Or is it some combination of many factors.? (Of course we are firing these loads from the same handgun)


Thanks to all for looking at my question.

 

[ken158]

Every action has an equal and opposite reaction and the more energy (weight and velocity) in one direction means more energy in the other direction. As the energy pushes back in your direction, the weight of the handgun will affect the amount of recoil you feel.

 

[505Gibbs]

Every action has an equal and opposite reaction and the more energy (weight and velocity) in one direction means more energy in the other direction. As the energy pushes back in your direction, the weight of the handgun will affect the amount of recoil you feel.

This is spot on!

 

[Dragon88]

Recoil Calculator

 

[Alk8944]

Kinetic energy is not a good indicator of recoil, momentum (mass[pounds] x velocity) is. Momentum of the bullet = gun momentum in all cases. There is one variable which is hard to quantify which how much of the weight of your body figures into mass of the revolver, since this mass also has to be accelerated it tends to reduce firearm momentum. It also explains why a revolver can seem to kick just as hard as a rifle that is generating several times as much muzzle energy.

One clarification too. What you are really looking for is "perceived recoil", what is seems to you to be. Two guns of the same weight, firing the same cartridge, at the same velocity, can feel much different. The difference between a Garand and Springfield is one good example.

To calculate momentum multiply bullet weight in pounds by velocity in FPS. Example, .357 Magnum, 158 gr bullet @ 1500 FPS: wt(158/7000 = .02257) x 1500 = 33.85 pound feet of momentum. This is the theoretical amount of energy directed into your hand. Or, for a M&P @ 850 FPS: same .02257 x 850 = 19.18 pound feet of momentum, a bit over 1/2 as much. Or a .500 S&W, 400 gr @ 1600 FPS: (400/7000 = .05714) x 1600 = 91.43 pound feet momentum. Much simpler than recoil energy in FPE, and more closely follows what you will actually feel.

Just for comparison, .30-06, 150 gr @ 2850 FPS, you know how to derive this now. Firearm momentum = 61.07 pound feet.

Perceived recoil will be mitigated/aggravated by such things as a heavier gun, energy absorbing grips/recoil pad, muzzle break, stock shape, etc.

 

[HoosierMike]

More goes into it than the math. Gun design plays a big part in percieved recoil. For instance. A S&W model 29 feels like it kicks much harder than say a Ruger Super Blackhawk. Or a Winchester 94 carbine in 30/30 seems like it kicks much harder than a Marlin 336 with the same load. IMHO.

 

[Silversmok3]

I agree that there is much more to the story than just the math.

Frame size matters.Shooting .45+P from a compact polymer gun will have sharper recoil than the same ammo fired from a full-length steel frame.

Another factor is energy 'spread'.The larger the gun, the more area the recoil energy is distributed and less of it is felt to the shooter as recoil.

To add a third wrinkle to the mix the shooter's grip plays a major part too. The same gun could recoil worse for two different shooters based on hand size and how the gun is thus gripped.

Just some thoughts on the subject.

 

[Sevastopol]

I'm pretty sure powder weight must be taken into account, too. Not sure what the math would be on that, since some is converted into heat?

 

[38-44HD45]

Powder weight does come into play. I've forgotten the formula, but I'll try to look it up tonight. In the conventional/traditional formula, the powder ejecta is assumed to have a velocity of 4000 fps., regardless of the velocity of the bullet. Obviously, this is an approximation, but it should tell you that small differences in powder charge weight may make larger than expected differences in recoil. A .45 ACP load pushing a 230gr. bullet at 800 fps. with 8 grains of powder will have a little more actual recoil and noticeably more felt recoil than one pushing the same bullet to the same velocity with 5 grains of powder. However, as so many of us learned in the old days of IPSC, the pressure curve of the powder also plays a part in the subjective part of the matter, so two loads with identical bullet and ejecta weight and the same velocity may "feel" different.

 

[Sevastopol]

Powder weight does come into play. I've forgotten the formula, but I'll try to look it up tonight. In the conventional/traditional formula, the powder ejecta is assumed to have a velocity of 4000 fps., regardless of the velocity of the bullet. Obviously, this is an approximation, but it should tell you that small differences in powder charge weight may make larger than expected differences in recoil. A .45 ACP load pushing a 230gr. bullet at 800 fps. with 8 grains of powder will have a little more actual recoil and noticeably more felt recoil than one pushing the same bullet to the same velocity with 5 grains of powder. However, as so many of us learned in the old days of IPSC, the pressure curve of the powder also plays a part in the subjective part of the matter, so two loads with identical bullet and ejecta weight and the same velocity may "feel" different.

Hi. Did you find the formula? I hope it doesn't just do a straight powder weight & velocity figure, as I don't think that would be correct.

Thanks.

 

[Dragon88]

Did you guys not see the link I posted? All this talk when the answer is sitting right there for you.

 

[Sevastopol]

Did you guys not see the link I posted? All this talk when the answer is sitting right there for you.

Thank you for that. I had skipped it, but I see now that I could take the max loads of two different weight bullets with the same powder in a particular load book and put them into that calculator. With a little math, it should give me an idea of how much the powder weight affects recoil, totally dependent, though, on the parameters used by this particular calculator.

Thanks again.

 

[Neumann]

Felt recoil is hard to define. The energy of recoil is easy enough to calculate using the tool provided in a previous post. The muzzle energy of the bullet (e = 1/2 mv^2) is divided between the bullet and pistol so that the momentum (mv) is the same in opposite directions. A heavier bullet will impart more recoil than a lighter bullet with the same energy. Assuming you are comparing different ammunition in the same gun, there are still some differences.

What you feel in the palm of your hand is not just energy, but force, and the same momentum delivered over a shorter period of time has more force. This means a faster, lighter bullet often has more felt recoil than a slower, heavier bullet with approximately the same recoil energy.

The slide in a pistol spreads this force over a relatively long period of time. Otherwise, you would have a hard time holding on to the little P45. It also evens out the effect of velocity, but not totally.

In a revolver, there's nothing to even out the recoil. Consequently you feel a real sting shooting 185 grain bullets at 1600 fps vs 240 grain bullets at 1200 fps in a .44 magnum, or 125 grain v 158 grain in a .357 magnum, even though the energy of recoil is about the same in each case (within that caliber).

 

[LedFowl]

The slide in a pistol spreads this force over a relatively long period of time. Otherwise, you would have a hard time holding on to the little P45. It also evens out the effect of velocity, but not totally.

In a revolver, there's nothing to even out the recoil. Consequently you feel a real sting shooting 185 grain bullets at 1600 fps vs 240 grain bullets at 1200 fps in a .44 magnum, or 125 grain v 158 grain in a .357 magnum, even though the energy of recoil is about the same in each case (within that caliber).

A .44 magnum Desert Eagle should have less perceived recoil than a revolver firing the same load (handgun weight being equal), is that correct? I'd never thought about this.

Does gas-operation have less perceived recoil than short-recoil operation, if round and pistol weight are equal?

 

[OKFC05]

I was going to refrain from posting in this thread, but I can't stand it anymore because the confusion in terms is beyond tolerating.

First, Dragon 88 posted the link to a recoil calculator which has an excellent explantion of terms, but apparently it is being ignored.
Recoil Calculator

It calculates Recoil Impulse, Velocity of recoiling firearm, and Free Recoil Energy.
Each of these is a different number, in different units.

The numbers calculated here do not relate to "felt recoil", which is highly subjective and cannot be measured. Felt recoil is different for each person, what is excessive for me might not be for you and vice versa. Due to the extreme possible variations in firearm design, grip design and people it will not give you a direct correlation from one firearm to another, for example a Smith and Wesson M29 with stock grips is going to have a far different felt recoil than a ported Ruger Super Redhawk using the same load. It will however give you a good idea how one load will feel compared to another in the same or similar firearm.